The present invention concerns a transition metal-catalyzed process for the production of monoalkyltin trihalides involving a redistribution reaction between tetraorganotins, triorganotin halides or diorganotin halides and tin tetrahalides.
Monoalkyltin trichlorides can be prepared industrially from tetraalkyltins and SnCl4 according to the stoichiometry of eq. 1 (Neumann, W. P.; Burkhardt, G. Liebigs Ann. Chem. 1963, 663, 11).
R4Sn+2 SnCl4xe2x86x922 RSnCl2+R2SnCl2xe2x80x83xe2x80x83(1)
R4Sn+3 SnCl4xe2x86x924 RSnCl3xe2x80x83xe2x80x83(2)
R2SnCl2+SnCl4xe2x86x922 RSnCl3xe2x80x83xe2x80x83(3)
(R=alkyl or cycloalkyl)
This process was further improved by MandT chemicals (Natoli, J. G., U.S. Pat. No. 3,432,531, 1969; Larkin, W. A.; Bouchoux, J. W., U.S. Pat. No. 3,931,264, 1976). In this process substantial amounts of dialkyltin dichloride are formed as by-product (typically around 33%).
The reason that the process according to eq. 1 is often used and not that of eq. 2, is that eq. 3 does not proceed under mild conditions for longer alkyl groups. Eq. 3 would be the last step in a process according to eq. 2.
Nothwithstanding the above remarks, Neumann (U.S. Pat. No. 3,459,779, 1969) has described the redistribution reaction of dialkyltin halides with SnCl4 in POCl3/P2O5 to produce monoalkyltin trichlorides. Also Langer et al. reported the formation of MeSnCl3 from dimethyltin dichloride and tin tetrachloride in dimethylsulfoxide (DMSO) (Tetrahedron Lett., 1967, 1, 43-47; U.S. Pat. No. 3,454,610, 1969, to Dow Chemical Co.). Also the redistribution of dialkyltin dihalides, trialkyltin halides or tetraalkyltins with tin tetrahalide catalyzed by quarternary ammonium salts at temperatures above 150xc2x0 C. has been reported (Kugele, T. G.; Parker, D. H., U.S. Pat. No. 3,862,198, 1975) and more recently, redistribution reactions of organotins catalyzed by SnF2 were claimed by Buschhoff et al. (U.S. Pat. No. 4,604,475, 1986, to Schering A. G.).
All the processes described above generally use harsh reaction conditions and yields are often less than desirable.
It is therefore an object of the current invention to provide for a catalytic process for the production of monoorganotin trihalides from tetraalkyltins or polyalkyltin halides and tin tetrahalide that can be operated under mild conditions (T less than 150xc2x0 C., pxe2x89xa65 bar) and which affords the product in high yield ( greater than 60% based on Sn).
It is also an object of the current invention to make use of transition metal complexes as pre)catalyst as opposed to previously reported catalysts.
In its broadest form the present invention comprises a process for the production of monoalkyltin trihalides of the formula RSnX3, wherein R=alkyl or cycloalkyl and Xxe2x95x90Cl, Br or I, involving a redistribution reaction between tetraorganotins, triorganotin halides or diorganotin halides and tin tetrahalides, said process comprising contacting tetra-(R4Sn), tri-(R3SnX) or diorganiotin halides (R2SnX2) with SnX4 to afford said monoorganotin trihalides in the presence of at least one transition metal complex, said complex comprising at least one transition metal, M, selected from Group VIII of the periodic Table of elements, at least one monodentate ligand or bidentate ligand, L or Lxe2x80x2, and optionally one or more anions, X, of an organic or inorganic acid, as a catalyst or catalyst precursor.
According to one embodiment of the invention, the catalyst is based on the use of a complex having the formula
xe2x80x83Lxe2x80x2MX2xe2x80x83xe2x80x83(I)
wherein Lxe2x80x2 is a bidentate ligand, or
L2MX2xe2x80x83xe2x80x83(II)
wherein L is a monodentate ligand, or
L4Mxe2x80x83xe2x80x83(III),
wherein L is a monodentate ligand.
According to another embodiment, the said complex is:
[Lxe2x80x3M(xcexcxe2x88x92X)]2 xe2x80x83xe2x80x83(IV)
wherein Lxe2x80x3=a cyclometallated bidentate optionally substituted o-(diarylphosphino)benz-yl ligand. Catalysts of type (IV) have been applied for the Heck-vinylation of aryl halides (EP 725049 A1).
The metal to be used is a Group VIII metal, and preferred metals are Pt, Pd and/or Ni. The anions may be of organic and/or inorganic nature. It is preferred to use Cl, Br, I, acetate, triflate or tosylate anions.
The current invention thus involves the use of transition metal complexes according to formula (I), (II), (III), or (IV) as a (pre-)catalyst in the redistribution reaction of tetra-(R4Sn), tri-(R3SnX) or diorganotin halides (R2SnX2) with SnX4 to afford monoorganotin trihalides (RSnX3; R=alkyl or cycloalkyl; Xxe2x95x90Cl, Br or I).
In a preferred embodiment of the invention L in formula (II) or (III) is selected from phosphine, alkene, amine, organic sulfide, nitrile and imidazoline-2-ylidene. Lxe2x80x2 is selected from diphosphine, dialkene, diamine and bis(imidazoline-2-ylidene) ligands, preferably optionally substituted o-{di(2-tolyl)phosphino}benzyl. More in particular L is triphenylphosphine or Lxe2x80x2=N,N,Nxe2x80x2,Nxe2x80x2-tetramethylethylenediamine (TMEDA), M is Pd or Pt and for catalyst (I), X is Cl.
The catalyzed redistribution reaction concerns the redistribution of Bu2SnCl2 or Bu4Sn with SnCl4 to afford BuSnCl3. The use of (pre)catalysts according to formula (I), (II), (III) and (IV) allows the formation of BuSnCl3 from redistribution of Bu2SnCl2 or Bu4Sn with SnCl4 under mild reaction conditions (Txe2x89xa6150xc2x0 C., pxe2x89xa61 bar) in less than 24 hours and better than 70% yield (based on Sn).
The group R is preferably defined as an alkyl (linear or branched), cycloaryl or aryl, having from 1 to 12 C-atoms. Preferably methyl, n-butyl or n-hexyl are used.
The reaction can be carried out with or without a solvent. In general inert organic and aprotic solvents are preferred, especially aromatic solvents, chloroaromatics, alkanes, dialkylacetamides, N-alkylpyrolidones, dialkylamides of aliphatic carboxylic acids and organic nitriles. In particular toluene, o-xylene, 1,2-dichlorobenzene and n-octane were found to be appropriate solvents.
In a specific embodiment of the invention the concentration of the tin reagents employed falls within the range of 0.01 to 5, more preferred 0.1-2.0 M
The catalyst loading based on the total amount of Sn used can be  less than 5% and even  less than 0.1%. The catalyst is preferably employed in the concentration range 5xc2x710xe2x88x924-0.1 M.
In one specific example, which employed PtCl2(PPh3)2 as catalyst (or catalyst precursor) in toluene at a reaction temperature of 85xc2x0 C., the yield of BuSnCl3 was found to be as high as 92% (based on Sn). SnCl2 was the sole tin-containing by-product.
In another preferred embodiment of the invention the catalyzed redistribution reaction concerns redistribution between R2SnCl2 or R4Sn (R is Me, Et, propyl, hexyl, more preferably Me and n-hexyl) and SnCl4 to afford RSnCl3. For R=Me and n-hexyl, the monoalkyltin trichloride was obtained starting from R2SnCl2 and SnCl4 in 87 and 67% yield, repectively, whereas in the blank experiment (no catalyst added) only unreacted starting materials were recovered.
The invention is now further demonstrated by the following examples.